The finishing of textile substrates, e.g. of synthetic leather based fleeces, with binders is frequently carried out in the known art with a thermosensitized binder liquor. In such a liquor, the binder used is a plastic dispersion which has been adjusted to be heat sensitive. After its introduction into the fleece, the material is heated, so that the binder is completely coagulated and thus fixed in the fleece without leaving a residue and localized. This may be followed by a squeezing off process to remove excess water, and the material is then dried and subsequently cross-linked or vulcanized.
For economic reasons, the materials which are strengthened in this way are in practice mainly comparatively thick fleeces which are split into individual layers after they have been treated with the binder. These stiff layers are then buffed to produce a smooth surface.
The synthetic leathers known in the art, which are manufactured by the process described above or by similar processes, have excellent mechanical properties but they generally do not have the water vapor absorption capacity of natural leather, which is very important for the comfort in wear of articles manufactured from such synthetic leather materials, particularly shoes.
There have therefore been many attempts to remedy this defect by subsequently impregnating the finished synthetic leather fleeces or combining the binders with hydrophilic additives.
It has not hitherto been possible to find a finish which not only increases the water vapor absorption capacity of synthetic leather but also has a combination of the following properties which are very important in practice:
(a) The finishing should not require an additional operating step, i.e. subsequent or previous impregnation and possibly drying and cross-linking of the finished fleeces is undesirable. PA1 (b) In order that the finish may be carried out in a single bath, the hydrophilising agent must be compatible with the binder and auxiliary agents. PA1 (c) The hydrophilising agent must not alter the coagulation point of the thermosensitive binder liquor for a period of several days nor may it deleteriously affect the running stability during impregnation, in order not to cause premature coating of the foulard rollers with coagulate produced by shearing forces during the finishing process. PA1 (d) The hydrophilising agent should be available in a liquid form so that it can easily be mixed with the other components. It must have a sufficiently low viscosity not to interfere with the impregnating process but must be sufficiently highly concentrated so that sufficient quantities thereof can be incorporated in a single process step. PA1 (e) The hydrophilising agent contained in the finishing liquor should be uniformly deposited in the fleece together with the binder in order to ensure homogeneous distribution. During the drying process, it should not migrate with the water which is removed by drying. The external surfaces of the article should not contain more hydrophilising agent than the core of the fleece so that the layers obtained by splitting do not differ from each other in their water storage capacity. PA1 (f) The hydrophilising agent applied to the fleece should be capable of being cross-linked and thereby rendered insoluble in water and should not be capable of being removed by dissolving when subsequently exposed to moisture. The cross-linking process should be completed under the conditions employed for cross-linking or vulcanizing the binder. PA1 (g) It is particularly important that the introduction of sufficient quantities of hydrophilising agent should not deleteriously affect the handle of the finished fleece and in particular it should not harden the fleece. PA1 (h) The processes of splitting and buffing which follow the finishing process should not be rendered more difficult, for example by the premature addition of buffing paper because the hydrophilising agent has thermoplastic properties.
None of the hydrophilising agents hitherto proposed meet all the requirements mentioned above; at most, they satisfy only some of them, so that the problem of finding a suitable hydrophilising agent remained.